Understanding physics of plastic solar cells key for cheap, flexible PV

Recent work published by researchers from the University of Montreal, Imperial College London and the University of Cyprus have shed light on the physics of how ‘plastic’ polymeric semiconductor solar cells operate on an atomic level.

Plastic solar cells generate and transfer electric charge in a manner that, on a basic level, is quite similar to the silicon solar cells we are more accustomed to. In order to generate electricity, a photoelectric material must absorb the energy from a single packet of light (called a ‘photon’) and use it to generate a ‘free’ electron in the device. The main difference with plastic solar cells is that the material through which the electric charges travel through are polymer chains, rather than a solid crystal structure as is the case for silicon.

The research team used ultrafast femtosecond-speed spectroscopy measurements to understand how the polymers (and the chemical bonds within them) change as electric charges are generated during the photoelectric process.

The measurements showed that the change in the polymer structure during the process of electron generation occurs very quickly, within around 300 femtoseconds (10-15 s), and stays in that same state for another 100,000 femtoseconds. To put these timescales in perspective, a femtosecond is to a second as a second is to 3.7 million years.

The senior author of the study, Carlos Silva of the University of Montreal, stated that: “A greater understanding of [how plastic solar cells work] will obviously enable better [plastic] solar panels to be designed in the future.” Konarka has previously demonstrated pilot production of polymer‑fullerene solar cells with efficiencies of only around 3-5%.

Plastic solar cells bring a number of intriguing advantages to the table, namely cheaper materials, scalable manufacturing processes (i.e. spray coating) and the ability to be deposited onto flexible materials such as outdoor umbrellas and tents. However, in addition to their low conversion efficiencies, they last only a few years as compared to the 20-plus years most commercial PV modules are rated for.

Despite these limitations, plastic solar cells may become a cheap and popular alternative if the development of this technology continues.

Top Image Credit: University of Montreal

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John Rodriguez